Swirl interruption seal teeth for seal assembly

ABSTRACT

A seal assembly for sealing between a rotating component and a stationary component in a turbomachine. The seal assembly includes a plurality of radially inwardly projecting, axially spaced teeth extending from the stationary component, wherein at least one of the plurality of teeth has at least one axially extending hole therethrough. Axial flow of an operating fluid through the holes acts as an air-curtain to interrupt swirl flow in a seal cavity, therefore reducing steam force that could act to destabilize rotordynamics.

BACKGROUND OF THE INVENTION

The present invention relates generally to a seal assembly, and moreparticularly to a seal assembly including at least one seal tooth havingat least one hole to reduce swirl-induced rotordynamic instability.

In rotary machines such as turbines, seals are provided between rotatingand stationary components. For example, in steam turbines, it iscustomary to provide a plurality of arcuate packing ring segments toform an annular labyrinth seal between the stationary and rotatingcomponents. Typically, the arcuate packing ring segments (typically,four to six per annular seal) are disposed in an annular groove in thestationary component concentric to the axis of rotation of the machineand hence concentric to the sealing surface of the rotating component.Each arcuate seal segment carries an arcuate seal face in opposition tothe sealing surface of the rotating component. In labyrinth type seals,a plurality of axially spaced, circumferentially extending seal teethextend from the stationary component toward the rotating component. Thesealing function is achieved by creating turbulent or flow restrictionof an operative fluid, for example, steam, as it passes through therelatively tight clearances within the labyrinth defined by the sealface teeth and the opposing surface of the rotating component.

In operation, with high rotor rotational velocity, fluid axiallyentering the fluid path of a rotary machine can acquire a significanttangential velocity component (also called “steam swirl”). For example,as the fluid moves through the labyrinth seal, the fluid may flowbetween the axially spaced seal teeth and circumferentially around therotating component. This causes the fluid to acquire the significanttangential velocity component, which can induce rotor instabilities inturbomachines. The magnitude of this rotor instability is a function ofthe circumferential flow component of fluid within the labyrinth seal.

As more and tighter seals are used in steam turbines, swirl-inducedrotordynamic instability becomes more critical for large steamapplications. Conventional anti-swirl teeth take up additional axialspace and are not rub-friendly, because the clearance has to be setlarge enough to avoiding rubbing against a rotor generating a lot ofheat. To reduce the risk of scoring the rotor, conventional sealsegments with anti-swirl features are typically assembled into astationary component with a spring element to allow the seal ring tomove away from the stationary component in case of rotor rubbing.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of this invention include a seal assembly for sealingbetween a rotating component and a stationary component in aturbomachine. The seal assembly includes a plurality of radiallyinwardly projecting, axially spaced teeth extending from the stationarycomponent, wherein at least one of the plurality of teeth has at leastone axially extending hole therethrough. Axial flow of an operatingfluid through the holes acts as an air-curtain to interrupt swirl flowin a seal cavity, therefore reducing steam force that could act todestabilize rotordynamics.

A first aspect of the invention provides a seal assembly for sealingbetween a rotating component and a stationary component in aturbomachine, the seal assembly comprising: a plurality of radiallyinwardly projecting, axially spaced teeth extending from the stationarycomponent, wherein at least one of the plurality of teeth has at leastone axially extending hole therethrough.

A second aspect of the invention provides a turbomachine comprising: arotating element; a stationary component substantially surrounding therotating element; and a seal assembly coupled to the stationarycomponent, the seal assembly including: a plurality of radially inwardlyprojecting, axially spaced teeth extending from the stationarycomponent, wherein at least one of the plurality of teeth has at leastone axially extending hole therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows a partial cross-sectional view of turbomachine including aseal assembly according to an embodiment of the invention.

FIG. 2 shows a cross-sectional view of a seal system according to anembodiment of the invention;

FIG. 3 shows partial perspective view of a seal assembly according to anembodiment of the invention;

FIG. 4 shows a cross-sectional view of a seal system according to anembodiment of the invention;

FIG. 5 shows cross-sectional views of various alternative geometries ofholes in a seal tooth, taken along view A in FIG. 2 and FIG. 4,according in embodiments of the invention;

FIG. 6 shows a close up perspective view of a seal tooth of a sealassembly according to an embodiment of the invention;

FIG. 7 shows a cross-sectional view of a seal tooth, taken along view7-7 in FIG. 6, according to an embodiment of the invention; and

FIG. 8 shows a cross-sectional view of a seal tooth, taken along view8-8 in FIG. 7, according to an embodiment of the invention.

It is noted that the drawings of the invention are not necessarily toscale. The drawings are intended to depict only typical aspects of theinvention, and therefore should not be considered as limiting the scopeof the invention. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Turning to FIG. 1, a partial cross-sectional view of a machine 10including a labyrinth seal 100 according to an embodiment of theinvention is shown. Although FIGS. 1-4 are shown and discussed withrespect to a steam turbine, it is understood that the teachings of thevarious embodiments of the invention may be similarly applied to otherturbomachines and that a steam turbine is merely used as an example ofone type of turbomachine to describe the aspects of the invention.

Turning to FIG. 1, turbomachine 10 includes a rotating element 102 and astationary component 104. Stationary component 104 may substantiallysurround rotating element 102. Turbomachine 10 also includes at leastone seal assembly 100 coupled to stationary component 104. As shown inFIG. 2, in one embodiment, seal assembly 100 may be coupled tostationary component 104 by fitting a mounting portion 106 of an arcuatepacking ring 108 within a groove 110 of stationary component 102.

Seal assembly 100 may include a plurality of arcuate packing rings 108(only one shown). Arcuate packing rings 108 may be configured to form anannulus that proximately surrounds rotating element 102. In theembodiment shown in FIG. 2, seal assembly 100 comprises a labyrinthseal, having a plurality of radially inwardly projecting, axially spacedteeth 112 extending from stationary component 104 toward rotatingcomponent 102. The plurality of seal teeth 112 can be coupled to eacharcuate packing ring 108. Plurality of seal teeth 112 may be coupled toeach arcuate packing ring 108 according to any now known or laterdeveloped manner, such as, but not limited to, embedded, caulked, ormachined. Plurality of seal teeth 112 extend in a radial directiontowards rotating element 102 and also in a circumferential directionaround rotating element 102, such that plurality of seal teeth 112 sealagainst flow leakage that may be present along machine 10 (FIG. 1). Asshown in FIG. 2, labyrinth seal system 100 has an upstream, highpressure side, P_(H), and a downstream, low pressure side, P_(L).Operating fluid from a turbomachine 10 (FIG. 1) flows through seal 100from high pressure side, P_(H), to low pressure side, P_(L).

As shown in FIG. 2, according to an embodiment of the invention, atleast one seal tooth 112 of plurality of seal teeth 112 may include ahole 114 that extends through seal tooth 112 in the axial direction ofrotating element 102. As discussed herein, at least one hole 114 acts toreduce the rotor induced swirl between the plurality of seal teeth 112and rotating element 102.

Each hole 114 can extend in an axial direction through a seal tooth 112,and a plurality of holes 114 can be included along a circumferentialdirection along an arcuate portion of seal teeth 112 (e.g., in anarcuate portion of seal assembly 100 shown in FIG. 3).

Holes 114 can comprise any shape or size desired. For example, threedifferent shape holes 114 can be seen in FIG. 5. In the first example,substantially cylindrical holes 114 are included through a seal tooth112. Cylindrical holes 114 can comprise substantially cylindrical,tubular holes through a seal tooth 112. In the second example, holes 114also comprise slots extending through seal teeth 112 in an axial as wellas circumferential direction. As shown in FIG. 5, a rounded slot orcut-out is made through a distal end of seal tooth 112, such that arounded, rectangular, tubular hole is formed through seal tooth 112. Inthe third example, a rounded cut-out is made similar to the secondexample, but in this example, the cut-out extends from a distal end ofseal tooth 112 into a substantial root of the seal tooth 112.

In one embodiment, holes 114 can extend through seal teeth 112substantially horizontally, i.e., parallel to a centerline of rotatingcomponent 102. In another embodiment, as illustrated in FIGS. 6-8, holes114 can extend through seal teeth 112 at an axial angle, i.e., notparallel to a centerline of rotating component 102. An angled hole 114could be used to increase a flow path of operating fluid through sealassembly 100, and/or to increase or decrease the swirl interruption asdesired. For example, the more axially angled the hole 114 is (i.e., themore angled away from parallel to rotating component 102 centerline),the longer the flowpath within hole 114 becomes, and the more effectiveswirl interruption will result. In one embodiment, holes 114 can beangled at an axial angle in the range of approximately 0 degrees toapproximately 90 degrees. As shown in FIGS. 6-8, holes 114 can be alsoangled circumferentially in tangential direction with respect to aradial direction and axial direction of rotating component 102 togenerate a circumferential velocity component against swirl flowdirection. In one embodiment, holes 114 can be angled at a tangentialangle in the range of approximately 0 degrees to approximately 60degrees.

Holes 114 can be included in any seal tooth 112 desired, but in oneembodiment, holes 114 can be included only in a first, upstream tooth112 (see, e.g., FIG. 3), or first and second upstream teeth 112 (see,e.g., FIG. 2). Including holes 114 in the upstream teeth 112 allows foradequate swirl reduction, as discussed herein, while also allowing thedownstream teeth 112 without holes to provide adequate sealing.

Seal teeth 112 that include holes 114 act as swirl interruption teeth,rather than primarily sealing teeth, since teeth 112 with holes 114allow operative fluid to flow therethrough. Therefore, the purpose ofteeth 112 with holes 114 is primarily to reduce swirl of operative fluidthrough seal assembly 110, rather than primarily to reduce operativefluid from passing between rotating component 102 and stationarycomponent 104 as is the function of seal teeth 112 without holes 114.

In one embodiment, holes 114 in adjacent seal teeth 112 can bepositioned circumferentially such that holes 114 are axially aligned forease of manufacture (as shown in FIG. 3), or in another embodiment,holes 114 can be staggered circumferentially such that holes 114 are notaligned, e.g., if holes 114 are drilled in a skewed anglecircumferentially.

In the embodiment shown in FIG. 4, the seal tooth 112 with anti-swirlholes 114 is an integral part of stationary component 104. Thisconfiguration has the additional benefit of a compact design. Incontrast, conventional anti-swirl features typically use axially angledteeth, which need significant axial width to be effective in turning theflow direction. Those conventional anti-swirl teeth are stiff and notrotor rub-friendly, and need to be implemented on a segmented packingring, which is installed into stationary component via a spring means toallow relative motion between seal segment and stationary component. Incontrast, the anti-swirl features disclosed in embodiments of thisinvention are implemented on a thin tooth, not a thicker, axiallyangled, tooth. Therefore, seal teeth 112 of the claimed invention can bean integral part of stationary component 104, or can be rigidlyattached, or linked, to a non-moving portion stationary component 104,without imposing risk of damaging rotating component 102. Therefore, inthe embodiment shown in FIG. 4, integral teeth 112 do not movetowards/away from rotating component 102.

In another embodiment, shown in FIG. 2, seal teeth 112 are mounted onpacking ring 108, and mounting portion 106 of packing ring 108 ispositioned within a circumferential groove 110 such that mountingportion 106 can move radially within groove 110. As in conventionallabyrinth seals, mounting portion 106 moves radially (e.g., using aspring, not shown) towards and away from rotating component, to moveseal teeth 112 to/away from rotating component 102.

Seal teeth 112 including holes 114 can act to move operating fluidmoving through seal assembly 100 through holes 114. This will create anair curtain effect, and the axial jet-flow through holes 114 willinterrupt swirl flow in the seal cavity, therefore improvingrotordynamics stability. Swirl interruption features described hereincan be used to mitigate field issue with rotordynamics. For example, ifa turbine is identified with high rotor vibration due to steam swirl,swirl interruption features (e.g., holes 114 as shown in FIG. 2 and FIG.4) can be easily added to existing inward teeth to reduce swirl.

As mentioned above, seal assembly 100 may be configured to form anannulus that proximately surrounds rotating element 102. Referring backto FIG. 1, seal assembly 100 may proximately surround any portion ofrotating element 102 that requires leakage prevention and swirlreduction. For example, seal assembly 100 may proximately surround rotor102. Alternatively, seal assembly 100 may proximately surround bucketassembly 124 to reduce bucket tip leakage and swirl.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

This written description uses examples to disclose the variousembodiments of the present invention, including the best mode, and alsoto enable any person skilled in the art to practice the invention,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the various embodiments ofthe present invention is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims.

What is claimed is:
 1. A seal assembly for sealing between a rotatingcomponent and a stationary component in a turbomachine, the sealassembly comprising: a plurality of radially inwardly projecting,axially spaced teeth extending from the stationary component, wherein atleast one of the plurality of teeth has at least one axially extendinghole therethrough, the axially extending hole extending through the atleast one of the plurality of teeth from an upstream, high-pressure sideto a downstream, low-pressure side of the at least one tooth and beingdistanced from a radially innermost surface of the at least one toothand positioned radially inwardly from a radially innermost surface of anarcuate packing ring, wherein the upstream, high-pressure side is influid communication with the downstream, low-pressure side via the atleast one axially extending hole.
 2. The seal assembly of claim 1,wherein the at least one tooth having an axially extending holetherethrough comprises a first tooth on the upstream, high pressureside.
 3. The seal assembly of claim 2, wherein the at least one toothhaving an axially extending hole therethrough comprises a first toothand a second tooth on the upstream, high-pressure side.
 4. The sealassembly of claim 1, wherein the plurality of teeth comprise arcuatesegments of teeth, the proximal end of the at least one toothcollectively extending continuously about the circumference of therotating component, and wherein the at least one hole comprises aplurality of circumferentially spaced holes along the arcuate portion ofteeth.
 5. The seal assembly of claim 1, wherein the at least one holeincludes a substantially cylindrical, tubular hole.
 6. The seal assemblyof claim 1, wherein the at least one hole extends axially through a sealtooth at an axial angle with respect to a centerline of the rotatingcomponent and at tangential angle with respect to a circumferentialdirection of the rotating component, wherein the axial angle is in therange of 0 degrees to 90 degrees and the tangential angle is in therange of 0 degrees to 60 degrees.
 7. The seal assembly of claim 1, theseal assembly having a plurality of arcuate portions, each arcuateportion including an arcuate packing ring, wherein each arcuate packingring is moveably mounted in a circumferential groove in the stationarycomponent.
 8. The seal assembly of claim 1, wherein the rotating elementis a rotor.
 9. A turbomachine comprising: a rotating element; astationary component substantially surrounding the rotating element; anda seal assembly coupled to the stationary component, the seal assemblyincluding: a plurality of radially inwardly projecting, axially spacedteeth extending from the stationary component, wherein at least one ofthe plurality of teeth has at least one axially extending holetherethrough, the axially extending hole extending through the at leastone of the plurality of teeth from an upstream, high pressure side to adownstream, low pressure side of the at least one tooth and beingdistanced from a radially innermost surface of the at least one toothand positioned radially inwardly from a radially innermost surface of anarcuate packing ring, wherein the upstream, high-pressure side is influid communication with the downstream, low-pressure side via the atleast one axially extending hole.
 10. The turbomachine of claim 9,wherein the at least one tooth having an axially extending holetherethrough comprises a first tooth on the upstream, high-pressureside.
 11. The turbomachine of claim 10, wherein the at least one toothhaving an axially extending hole therethrough comprises a first toothand a second tooth on the upstream, high-pressure side.
 12. Theturbomachine of claim 9, wherein the plurality of teeth comprise arcuatesegments of teeth, the proximal end of the at least one toothcollectively extending continuously about the circumference of therotating component, and wherein the at least one hole comprises aplurality of circumferentially spaced holes along the arcuate portion ofteeth.
 13. The turbomachine of claim 9, wherein the at least one holeincludes a substantially cylindrical, tubular hole.
 14. The turbomachineof claim 9, wherein the at least one hole extends axially through a sealtooth at an axial angle with respect to a centerline of the rotatingcomponent and at tangential angle with respect to a circumferentialdirection of the rotating component, wherein the angle is in the rangeof 0 degrees to 90 degrees, and the tangential angle is in the range of0 degrees to 60 degrees.
 15. The turbomachine of claim 9, the sealassembly having a plurality of arcuate portions, each arcuate portionincluding an arcuate packing ring, wherein each arcuate packing ring ismoveably mounted in a circumferential groove in the stationarycomponent.
 16. The turbomachine of claim 9, wherein the rotating elementis a rotor.
 17. (The turbomachine of claim 9, wherein the seal assemblyis an integral part of the stationary component.
 18. The turbomachine ofclaim 9, wherein the seal assembly is rigidly attached to the stationarycomponent.